Mutex or spinlock? Which to use when
The exact semantics of learning to use the mutex lock and the spinlock are quite simple (with appropriate abstraction within the kernel API set making it even easier for the typical driver developer or module author). The critical question in this situation is a conceptual one: what really is the difference between these two lock types? More to the point, under which circumstances should you use which lock? You will learn the answers to these questions in this section.
Taking our previous driver read method’s pseudocode (Figure 12.6) as a base example, let’s say that three threads – tA, tB, and tC – are running in parallel (on an SMP system) through this code. We shall solve this concurrency issue, while avoiding any data races, by taking (acquiring) a lock prior to the start of the critical section (time t2), and releasing the lock (unlock) just after the end of the critical section code path (time t3). Let’...
